use Class::CGI
    handlers => {
      invoice_date => 'My::Date::Handler',
      sales_date   => 'My::Date::Handler',
    };
  my $cgi  = Class::CGI->new;
  my $date = $cgi->param('invoice_date');
  my $date = $cgi->param('sales_date');
  my $day  = $date->day;

##</code><code>##

  use Class::CGI
    handlers => {
      invoice_date => ['My::Date::Handler', qw(invoice_month invoice_day invoice_year)],
      sales_date => ['My::Date::Handler', qw(sales_month sales_day sales_year)],
    };
  my $cgi  = Class::CGI->new;
  my $date = $cgi->param('invoice_date');
  my $date = $cgi->param('sales_date');
  my $day  = $date->day;

##</code><code>##

package My::Date::Handler;

  use My::Date;

  sub new {
      my ($class, $cgi, $param) = (shift,shift,shift);  #standard
      my ($month, $day, $year)  = (shift,shift,shift);  #extra
      return My::Date->new(
        month => $month,
        day   => $day,
        year  => $year,
      );
  }
  1;

##</code><code>##

  use Class::CGI
    handlers => {
      customer_id => 'My::Customer',
      referral_id => 'My::Customer',
      sales_date => ['My::Date::Handler', 
                      qw(sales_month sales_day sales_year)],
    };
  my $cgi  = Class::CGI->new;
  my $sales_date = $cgi->param('sales_date');
  my $customer = $cgi->param('customer_id');
  my $referrer = $cgi->param('referrar_id');